Artificial abrasive articles



, abrasive art.

United States Patent Q ARTIFICIAL ABRASIVE ARTICLES Richard 0. Lane,Munith, Mich., assignor to M & M Research and Development Company,Jackson, Mich, a corporation of Michigan No Drawing. ApplicationDecember 7, 1954 Serial No. 473,762

4 Claims. (Cl. 51-298) The present invention relates to improvements inabrasive articles and the manufacture thereof, being acontinuation-in-part of copending application Serial No. 314,072, filedOctober 10, 1952.

It has heretofore been proposed, as disclosed in the Hartman Patent No.1,830,757, granted November 10, 1931, to employ an additive material inthe manufacture of abrasive articles to produce an abrasive wheel or thelike having self dressing characteristics to control glazing. Theadditive material contemplated by Hartman was not comparable to theabrasive grain forming the body of the articles in any physicalrespects. According to Hartmans disclosure the additive functioned toprovide ,voids by being more friable than the abrasive grains and bybeing of a less hardness yet capable of being broken out of the moldedmass of abrasive grains to leave an irregular face. Thus, theself-dressing was effected by the bodily displacement of the additive toleave a void.

In contrast to the disclosure of the aforesaid Hartman patent, thepresent invention contemplates an additive material in the form ofabrasive grains which are comparable in physical respects to theabrasive grains of the mother matrix.

In the form of loosely or weakly bonded abrasive grains dispersed Withinthe mother matrix, the additive, according to the present invention, isbodily dislodged by the action of the work piece presented to theworking face of the abrasive article; the

. present theory being that the self-dressing results from themechanical fracturing action of the additive upon the abrasive grains ofthe mother matrix taking place between the work piece and the workingface of the abrasive article.

In practicing the present invention, only the form and manner ofassociation of the additive in the mother matrix distinguishes themanufacture of abrasive articles made according to the invention overstandard practices in the This holds true without regard to the form ofbond of the mother matrix such as vitrified, resinoid, shellac, rubber,silicate, magnesium, oxychloride and metallic.

Being mechanical in nature, the action of the loosely or weakly bondedabrasive additive upon the firmly bonded abrasive body is relativelyindependent of the type of bonding so long as the bonding and/ orprocessing of the firmly bonded abrasive body does not destroy thefunctional characteristics of the dispersed loosely or weakly bondedabrasive additive.

Thus, an object of the invention is to provide an improved abrasivearticle having self-dressing characteristics in use in which a dispersedadditive is present in the form of loosely or weakly bonded abrasivegrains comparable in physical respects to the firmly bonded abrasivegrains of the main body of the abrasive article.

Another object of the invention is to provide an improved abrasivearticle of the type described in the preceding paragraph in which theadditive is in the form of pellets of loosely or weakly bonded abrasivegrains dispersed in the firmly bonded matrix of the abrasive article iceand the grains of which are readily and bodily dislodged during use ofthe abrasive article to function as a freed fracturing agent of thefirmly bonded abrasive grains of the matrix at the point of contactbetween the work piece and the abrasive article.

Another object is to provide, as a new article of manufacture, animproved additive for grinding wheels and the like to provide the samewith self-dressing characteristics, in the form of pellets or loosely orweakly bonded grains comparable in physical respects to the abrasivegrains making up the firmly bonded matrix.

These and other objects and advantages of the present invention willmore fully appear from the following specification and appended claims.

In carrying out the present invention the additive for abrasive articlespreferably comprises abrasive grains which are comparable in hardnessand resistance to fracture to the abrasive grains of the firmly bondedbody which make up and provide the structural mass of the abrasivearticle.

As it is the practice, for example, in the manufacture I of grindingWheels to make wheels of many sizes of abrasive grains, it would not bepractical to match the grain size of the additive with the grain size ofeach wheel in which the additive is used. It has been found in practicethat it is not necessary to closely match the size of the abrasive grainof the additive with the abrasive grain of the firmly bonded matrix ofthe wheel in order to obtain good results. For example, with theadditive having an abrasive grain size of 80, good results are obtainedwhen the additive is used in grinding wheels having abrasive grain sizesranging from 16 to 120. Likewise,

with a grain size of used inthe additive, good results have beenobtained from this additive when used in grinding Wheels having grainsizes ranging from 150 to 500.

The additive is preferably molded or shaped into pellets by anSXlII'IlSlODPIOCESS which is facilitated by having the additive mixsomewhat sticky and greasy. A typical additive mix would comprise 11,360grams of 80,grain size green or black silicon carbide; cornstarch 675grams; carboxyl methyl cellulose 575 grams; a colloidal type clay suchas bentonite 350 grams; glycerin 1000 cc.; and water The cornstarch,clay and carboxyl methyl cellulose are first dry blended and then theseare added to the water and glycerin to form a sticky mass. To this isslowly added the abrasive grains. Thereafter, the mix is agitated untila suitable consistency for extrusion is obtained. This mix is thenintroduced into a pug mill and extruded through holes and cut to Alength to provide the pellets.

The extruded and cut to length pellets are then dried to removesubstantially all moisture and thereafter subjected to a calciningoperation to eliminate the volatile materials, leaving a complexmagnesium aluminum silicate bond, holding the abrasive grains togetherwith a degree of tenacity which may be characterized as loosely orweakly bonded as compared to the bonding of the abrasive grains in thematrix of the grinding wheel. After calcining the pellets may bescreened and graded to provide a uniform product with the pelletsranging roughly in size from Me" to for use in grinding wheels of adiameter in the range of 4" and over. With smaller diameter wheels thepellet size should be proportionately reduced to permit uniformdispersion of the pellets with the matrix.

It is to be understood that the binding materials for the abrasivegrains of the pellets may be numerous. In the example given only thebentonite will be present in the pellets after calcining as a functionalresidue of any consequence. The other ingredients provide wetting,

lubricating and filler rolesto enable the pellets to be exused in'makingthepllets. As for example, in making the pellets the bonding materialwould be reduced to the order of 2% of the abrasive grain as compared to15 of'the abrasive grain going to make upthe matrix.

To give a typical example of the use'of the additive pellets in themanufacture of grinding wheels, 134 lb. 7

oz. of green or black silicon carbideof 46 size grain is mixed with 1640cc. of a solution of dry dextrine in water (50% dry dextrine and 50%water, approximate) until all 'the grain is uniformly wetted.Thereafter, 37 lb., 12 oz. of A3" to size pellets (previously calcinedand graded) are carefully and uniformly dispersed in the wetted abrasivegrains which make up the main body of the grinding wheels. Thisdispersion should be carried out with care to avoid any appreciablecrushing or disintegration of the pellets.

The bond for the abrasive grain of the matrix of the grinding wheel inthe example being given comprises 16 lb. '13 oz. of the followingingredients in the proportion given:

Percent Feldspar 57.35 Kentucky clay 17.50 Stoneware clay 17.50 Silica7.65

With this bond is hand-blended 5 lb. 11 /2 oz. of dry dextrine and theblended bond and dextrine is then added to the mixture of the precedingparagraph and a final mixing takes place to provide a uniform blend withthe pellets uniformly dispersed therein. This final mixture is thenremoved to the press room where 3,221 grams of the final mixture isplaced in a steel mold of the proper shape to make a 10.250" by 2.250 by7.025 wheel.

The wheel mold is then placed in av hydraulic press and pressure applieduntil the prescribed thickness is obtained, namely, 2.250"; the tonnagerequired to carry out this operation being in the order of 1000 to 2000per square inch of pressing surface.

Following inspection, the pressed wheel is then placed in a humiditydryer to remove the moisture. After being thoroughly dried thevitrification cycle is then carried out for nine days in a tunnel kilnin a well known manner. Thereafter the wheel is sized to by 2" by 7 andmounted upon a steel backing disc and placed in use.

In the example given above it will be noted that the pellets constitute20% by weight of the batch of the final mixture. Experimentation to dateindicates that the per-- centage of the pellets used may be varied overa rather Wide range without materially effecting the improvedperformance of the grinding wheels. However, good practice wouldindicate that the range should be in the order of 15% to for best allaround results.

It is to be understood that the bonding material for the 46 sizeabrasivegrain of the example given will firmly bond these grains into.the main mother matrix of the resulting grinding wheel in theconventional manner.

However, the bonding of the pellets in the matrix will be confined to aboundary'or skin bonding with the result that the interior abrasivegrains of the pellets will retain their original'loosely or weaklybonded state. Thus, the 46 size abrasive grains of the mother matrixwill all be firmly bonded together while the 80 size abrasive grains ofthe pellets will be loosely or weakly bonded in the wheel except for theboundary bonding that takes place between the mother matrix and theexterior grains of the pellets.

In the appended claims the term pellets is used to designate the smallpreformed objects made up of a relatively large. number of abrasivegrainsor crystals 4 bonded together to provide the additive which ismixed into the batch from which the abrasive article 'is later moldedand cured.

I claim:

1. An abrasive article of the type in which the components thereof arebatch mixed, molded into shape and cured to provide the structural formof the article consisting essentially of a main body portionconstituting the mother matrix of the article, said main body portionbeing formed of abrasive grains and bonding'material therefor, saidabrasive grains being firmly and independently bonded to each other toprovide thernother matrix with said abrasive grains being the mainabrasive grains of the abrasive article and providing in their bondedstate the structural strength and wearing surface of the article,pellets of abrasive grain and bonding material, the abrasive grains ofsaid pellets being of similar hardness and resistance to fracture assaid main abrasive grains, said pellets being present in said matrix asa batchmixed dispersed additive, the abrasive grains of said pelletsbeing weakly bonded to'each other, the bonding material and the amountthereof used in said pellets weakly retaining the abrasive grains ofsaid pellets in bonded association with each other as compared to thefirm bonding of said main abrasive grains to each other in said matrix,said abrasive grains of said pellets being of a size and being presentin sufficient number in said pellets to provide exteriorly located aswell as interiorly located grains,"the exteriorly located grains of saidpellets having boundry bonding in said matrix with the interiorlylocated grains of said pellets being free from bonding with said matrix,said interiorly located grains in said pellets being subject to bodilydislodgment in the working surface of said article when in use morereadily than said main abrasive grains in said matrix, the abrasivegrains of said matrix and saidpellets having a hardness of 9 orhigheronjthe Mobs scale, said pellets being of a size substantially to indiameter, and said'pellets constituting in the order of 15% to 25% byweight of the mixture from which the article is molded.

2. An abrasive article as defined in claim 1 in which the main abrasivegrains have a size in the range of 16 to and the size of the abrasivegrains of the pellets are substantially 80.

3. An abrasive article as defined in claim 1 in which the main abrasivegrains have a size in the range of'150 to 500 and the size of theabrasive grains .of the pellets are substantially 150.

4. An abrasive article as defined in claim 1 wherein the interiorabrasive grains of the pellets are bonded to each other with a tenacitycomparable to that resulting from a reduction in bonding material of 15%to 20% of the bonding material of the matrix to provide the weak bondingof the abrasive grains of the pelletsin contrast to the firm bonding ofthe abrasive grains of the matrix.

References Cited in the file of this patent UNITED STATES PATENTS1,133,739 Morse Mar. 30, 1915 1,830,757 Hartman Nov. 10, 1931 2,162,600Ball June '13, 1939 2,246,362 Kehoe et al June 17, 1941 2,334,266Houchins Nov. 16, 1943 2,463,679 Buckey Mar. 8, 1949 FOREIGN PATENTS163,179 Germany Dec. 7, 1902 172,813 Germany July 3, 1906 OTHERREFERENCES Websters New International Dictionary, 2nd edition, pp.1715-1716, 1940.

1. AN ABRASIVE ARTICLE OF THE TYPE IN WHICH THE COMPONENTS THEREOF AREBATCH MIXED, MOLDED INTO SHAPE AND CURED TO PROVIDE THE STRUCTURAL FORMOF THE ARTICLE CONSISTING ESSENTIALLY OF A MAIN BODY PORTIONCONSTITUTING THE MOTHER MATRIX OF THE ARTICLE, SAID MAIN BODY PORTIONBEING FORMED OF ABRASIVE GRAINS AND BONDING MATERIAL THEREFOR, SAIDABRASIVE GRAINS BEING FIRMLY AND INDEPENDENTLY BONDED TO EACH OTHER TOPROVIDE THE MOTHER MATRIX WITH SAID ABRASIVE GRAINS BEING THE MAINABRASIVE GRAINS OF THE ABRASIVE ARTICLE AND PORVIDING IN THEIR BONDEDSTATE THE STRUCTURAL STRENGTH AND WEARING SURFACE OF THE ARTICLE,PELLETS OF ABRASIVE GRAIN AND BONDING MATERIAL, THE ABRASIVE GRAINS OFSAID PELLETS BEING OF SIMILAR HARDNESS AND RESISTANCE TO FRACTURE ASSAID MAIN ABRASIVE GRAINS, SAID PELLETS BEING PRESENT IN SAID MATRIX ASA BATCH MIXED DISPERSED ADDITIVE, THE ABRASIVE GRAINS OF SAID PELLETSBEING WEAKLY BONDED TO EACH OTHER, THE BONDING MATERIAL AND THE AMOUNTTHEREOF USED IN SAID PELLETS WEAKLY RETAINING THE ABRASIVE GRAINS OFSAID PELLETS IN BONDED ASSOCIATION WITH EACH OTHER AS COMPARED TO THEFIRM BONDING OF SAID MAIN ABRASIVE GRAINS TO EACH OTHER IN SAID MATRIX,SAID ABRASIVE GRAINS OF SAID PELLETS BEING OF A SIZE AND BEING PRESENTIN SUFFICIENT NUMBER IN SAID PELLETS TO PROVIDE EXTERIORLY LOCATED ASWELL AS INTERIORLY LOCATED GRAINS, THE EXTERIORLY LOCATED A WELL ASINTERIORLY LOCATED GRAIN, THE BONDING IN SAID MATRIX WITH THE INTERIOLYLOCATED GRAINS OF SAID PELLET BEINGS FREE FROM BONDIND WITH SAID MATRIX,SAID INTERIORLY LOCATED GRAINS IN SAID PELLETS BEING SUBJECT TO BODILYDISLODGMENT IN THE WORKING SURFACE OF SAID ARTICLE WHEN IN USE MOREREADILY THAN SAID MAIN ABRASIVE GRAINS IN SAID MATRIX, THE ABRASIVEGRAINS OF SAID MATRIX AND SAID PELLETS HAVING A HARDNESS OF 9 OR HIGHERON THE MOHS SCALE, SAID PELLETS BEING OF A SIZE SUBSTANTIALLY 1/3" TO3/16" IN DIAMETER, AND SAID PELLETS CONSTITUTING IN THE ORDER OF 15% TO25% BY WEIGHT OF THE MIXTURE FROM WHICH THE ARTICLE IS MOLDED.